LOS ANGELES — John Dickerson, co-anchor of “CBS Evening News,” said Monday he will exit the network at the end of the year.

Dickerson will be the first major talent departure since the arrival of Bari Weiss as editor-in-chief of CBS News last month.

The veteran political journalist who joined CBS News in 2009 gave no reason for leaving in an Instagram post announcing his decision.

“I am extremely grateful for all that CBS News gave me — the work, the audience’s attention and the honor of being a part of the network’s history — and I am grateful for my dear colleagues who’ve made me a better journalist and a better human being and I will miss you,” Dickerson wrote.

Dickerson became co-anchor of “CBS Evening News” in January alongside Maurice DuBois, succeeding Norah O’Donnell. The duo were part of a revamp of the program, which put an emphasis on more in-depth stories.

The format change failed to attract new viewers as it remains in third place behind “ABC World News Tonight with David Muir” and “NBC Nightly News with Tom Llamas.”

There had been talk of significant changes coming to the newscast before Weiss signed on for a senior role at the division.